The present invention relates to an apparatus and method for peeling and separating adherent films. More particularly it relates to the peel development of photosensitive articles useful as color proofing films and printed circuit boards.
Many photosensitive articles are known in the art which are produced according to the "peel apart development" method. Typically, in the production of color proofing films and printed circuit boards, a substrate is first coated with an adherent image-forming material. This material is then covered with a transparent film in a sandwich construction. The construction is then imagewise exposed to actinic radiation through an exposure mask. Such exposure causes an image forming differential adhesion of the photosensitive layer such that part of the image adheres with a greater force to the substrate and part adheres preferentially to the cover film. When the cover film and substrate are "peeled apart" one finds, for example, a positive image reproduction remains on the substate and a negative reproduction appears on the top cover sheet.
In some laminating processes, it is desired to completely transfer a coating from one surface to another surface. For example, one may wish to transfer a colored resinous layer disposed on a substrate onto a receiver sheet. In such cases it is typical to juxtapose the coated substrate to the receiver sheet and pass this sandwich through the nip of a pair of heated laminating rollers under pressure. The substrate and receiver sheet are then peeled apart and the colored resinous layer is found to be transferred from the substrate to the receiver sheet. Those skilled in the art of layer transfer are well aware of the multitude of potential applications for such processes wherein the transferred layer may or may not be photosensitive or colored, and wherein single or plural layers are used and wherein full layers or differential images are actually transfered. Examples of such processes may be found in U.S. Pat. Nos. 3,721,557; 3,671,236; 4,247,614; 2,409,564 and 3,307,950 which are incorporated herein by reference.
One problem with such peel transfer methods is incomplete layer transfer. That is, most of the desired layer or image is correctly transferred to its desired receptor sheet but wherein there are certain "voids" or defects are produced. In the case of a full layer transfer, this problem manifests itself by a number of holes in the transferred layer. In the case of image transfer of photosensitive materials, cohesive stresses cause a loss of sharp image lines or image materials in nonimage areas or vice-versa.
U.S. Pat. No. 4,504,571 describes the importance of the angle at which the layers are peeled apart and the role such may play in successful layer separation. This reference suggests a peel angle (a) within the range of 0.degree..ltoreq.a.ltoreq.90.degree. and teaches one not to use higher peel angles in order to avoid deformations.
It has been found that a significant cause of the aforementioned voids is the production of a static charge during the separation process. The instant invention solves the incomplete separation problem by dissipating electric charge build-up during the peeling operation.